LASER BEAM IRRADIANCE CONTROL SYSTEMS
Irradiance control systems (“ICSs”) that control the irradiance of a beam of light are disclosed. ICSs include in a beam translator and a beam launch. The beam translator translates the beam substantially perpendicular to the propagating direction of the beam with a desired displacement so that the beam launch can remove a portion of the translated beam and the beam can be output with a desired irradiance. The beam launch attenuates the irradiance of the beam based on the amount by which the beam is translated. ISCs can be incorporated into fluorescent microscopy instruments to provide high-speed, fine-tune control over the irradiance of excitation beams.
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This application claims the benefit of Provisional Application No. 61/447,711; filed Mar. 1, 2011.
TECHNICAL FIELDThis disclosure relates to external systems for laser beam irradiance adjustment and control.
BACKGROUNDLaser beam irradiance adjustment and control can be difficult to achieve over an irradiance range of one order of magnitude or more. Even within this range, the accuracy and stability in the irradiance of the light output from a typical laser is often suboptimal for certain applications. Typical solutions for controlling the irradiance of a laser include controlling the current applied to the source or placing neutral density filters in the laser beam path to reduce the beam irradiance. In recent years, laser shutters have been optimized for speed by reducing the size of the shutters and by increasing the electrical power used to the control the shutters. As a result, laser shutters can be placed in the laser beam path to turn the laser beam “on” and “off.”
However, current control, density filtering, and use of shutters to adjust and control the irradiance of a laser beam is not optimal, especially when adjusting the laser on the sub-millisecond time scale is desired. For instance, the response time of a laser to a linearly controlled power source is typically non-linear, which limits the range of adjustability to about one order of magnitude. In addition, the temperature of a typical laser may fluctuate during operation, resulting in further irradiance instability. Neutral density filters may improve the irradiance range by several orders of magnitude, but filters provide only coarse irradiance adjustment, and typical high speed shutters are not capable of achieving sub-millisecond open and close times despite the reduced size of the aperture and higher driving voltages. For the above described reasons, engineers and scientists who develop and work with instruments that relay on high-speed control of laser light irradiance continue to seek mechanisms for laser beam irradiance adjustment and control on the sub-millisecond time scale.
SUMMARYIrradiance control systems (“ICSs”) that control the irradiance of a beam of light are disclosed. ICSs include in a beam translator and a beam launch. The beam translator translates the beam substantially perpendicular to the propagating direction of the beam with a desired displacement so that the beam launch can remove a portion of the translated beam and the beam can be output with a desired irradiance. The beam launch attenuates the irradiance of the beam based on the amount by which the beam is translated. ISCs can be incorporated into fluorescent microscopy instruments to provide high-speed, fine-tune control over the irradiance of excitation beams.
As shown in
In
In
Allowing the beam 302 to strike the plate 202 to cut off a portion of the beam 302 irradiance, as described above with reference to
The single-mode optical fiber 208 provides spatial filtering of the asymmetrical beams output from the lens 206. For example, as described above with reference to
In alternative embodiments, the single-mode optical fiber of the beam launch can be replaced by a plate with a diffraction-limited pinhole aperture, also referred to as a spatial filter.
For each rotational position of the pivot mirror 308 that results in the beam 700 being placed on one of the parallel paths, the beam 400 is reflected off of the pivot mirror 308 two times, the first stationary mirror 304 one time, and the second stationary mirror 306 one time for a total of four reflections.
When the beam translator 600 is implemented with a galvanometer mirror for the scanning mirror 602 sub-millisecond translation of the output beam is attainable, while typical shuttering times are around 0.2 milliseconds. Additionally, the translator 600 provides an effective means of implementing power control and power stabilization when optical feedback is present, as described above with reference to
The example beam translators 600, 900 and 1000 also preserve s- and p-polarization of the incident beam (i.e., s-polarization refers to light with electric field component direction perpendicular to the plane of the mirrors 604, 606 and 608). In other words, when a beam is input to the translators 600, 900 and 1000 with either s-polarization or p-polarization, the polarization of the beam is preserved as the beam is reflected off of the mirrors 604, 606 and 608.
ICSs can be incorporated into fluorescent microscopy instruments to control and adjust the irradiance of an excitation beam.
The lens 1106 focuses the excitation beam and the dichroic mirror 206 reflects the excitation beam into the back of the objective lens 1110. A portion of the fluorescent light emitted from fluorophores in the specimen 1120 are captured and collimated by the objective lens 1110 into a beam, represented by a shaded region 1122, that passes through the dichroic mirror 1108, and is focused onto the detector 1116 by the lens 1114. The detector 1116 can be a photomultiplier, photodiode, or a solid-state charged coupled device (“CCD”). Alternatively, the dichroic mirror 1108 can be configured to transmit the excitation beam and reflect the fluorescent light, in which case the locations of the ICS 1104 and the light source 1102 are switched with the lens 1114 and the detector 1116.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the disclosure. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the systems and methods described herein. The foregoing descriptions of specific examples are presented for purposes of illustration and description. They are not intended to be exhaustive of or to limit this disclosure to the precise forms described. Obviously, many modifications and variations are possible in view of the above teachings. The examples are shown and described in order to best explain the principles of this disclosure and practical applications, to thereby enable others skilled in the art to best utilize this disclosure and various examples with various modifications as are suited to the particular use contemplated. It is intended that the scope of this disclosure be defined by the following claims and their equivalents:
Claims
1. A system to control irradiance of a beam of light, the system comprising:
- a beam translator to translate the beam substantially perpendicular to a propagation direction of the beam with a desired displacement; and
- a beam launch located in the path of the translated beam, the launch to receive the translated beam and to attenuate the beam based on the amount by which the beam is to be translated.
2. The system of claim 1 further comprising:
- a feedback control electronically connected to the beam translator; and
- a splitter located in the path of the attenuated beam, the splitter to reflect a first portion of the attenuated beam to the feedback control and transmit a larger second portion, wherein the feedback control is to measure the irradiance of the first portion and direct the translator to translate the beam with the desired displacement based on the irradiance of the first portion.
3. The system of claim 1, wherein the beam translator includes:
- a scanning mirror; and
- at least two stationary mirrors, wherein the mirrors are positioned so that when the beam initially strikes the scanning mirror, the beam is reflected by the stationary mirrors and reflected a second time off of the scanning mirror to emerge on one of a continuum of substantially parallel paths.
4. The system of claim 1, wherein the beam undergoes four reflections prior to being output from the translator with the desired displacement.
5. The system of claim 1, wherein the beam translator includes a mirror attached to a motor, wherein the mirror is located in the path of the beam and angled to reflect the beam with a non-zero angle of reflection and the motor is to translate the mirror so that the beam is to be reflected onto one of a continuum of substantially parallel paths.
6. The system of claim 1, wherein the beam translator includes a transparent plate attached to a motor, wherein the transparent plate is to be located in the path of the beam and the motor is to rotate the plate so that beam is to be refracted and emerge on one of a continuum of substantially parallel paths.
7. The system of claim 1, wherein the beam launch includes:
- a plate with an aperture;
- a single-mode optical fiber; and
- a focusing lens disposed between the plate and a butt end of the fiber, wherein optical axes of the lens and the fiber are aligned and the aperture center is position along the optical axes, and wherein the butt end of the fiber is spaces from the lens so that the fiber acceptance cone cross-sectional dimensions approximately equal to size of the aperture.
8. The system of claim 1, wherein the beam launch includes:
- a first plate with an aperture;
- a second plate with a diffraction-limited pinhole aperture or spatial filter; and
- a focusing lens disposed between the first plate and the second plate, wherein the aperture centers are located along the optical axis of the lens.
9. The system of claim 1, wherein the beam translator is to translate the beam with the desired displacement in less than one millisecond.
10. A fluorescent microscopy instrument comprising:
- a light source to emit an excitation beam;
- a beam translator to translate the beam substantially perpendicular to a propagation direction of the beam with a desired displacement;
- a beam launch located in the path of the translated beam, the launch to receive the translated beam and to attenuate the beam based on the amount by which the beam is to be translated; and
- an objective lens to receive the attenuated beam and focus the attenuated beam to a focal point within a focal plane of a specimen.
11. The instrument of claim 10 further comprising:
- a feedback control electronically connected to the beam translator; and
- a splitter located in the path of the attenuated beam, the splitter to reflect a first portion of the attenuated beam to the feedback control and transmit a larger second portion, wherein the feedback control is to measure the irradiance of the first portion and direct the translator to translate the beam with the desired displacement based on the irradiance of the first portion.
12. The instrument of claim 10, wherein the beam translator includes:
- a scanning mirror; and
- at least two stationary mirrors, wherein the mirrors are positioned so that when the beam initially strikes the scanning mirror, the beam is reflected by the stationary mirrors and reflected a second time off of the scanning mirror to emerge on one of a continuum of substantially parallel paths.
13. The instrument of claim 10 or 12, wherein the beam undergoes four reflections prior to being output from the translator with the desired displacement.
14. The instrument of claim 10, wherein the beam translator includes a minor attached to a motor, wherein the mirror is located in the path of the beam and angled to reflect the beam with a non-zero angle of reflection and the motor is to translate the mirror so that the beam is to be reflected onto one of a continuum of substantially parallel paths.
15. The instrument of claim 10, wherein the beam translator includes a transparent plate attached to a motor, wherein the transparent plate is to be located in the path of the beam and the motor is to rotate the plate so that beam is to be refracted and emerge on one of a continuum of substantially parallel paths.
16. The instrument of claim 10, wherein the beam launch includes:
- a plate with an aperture;
- a single-mode optical fiber; and
- a focusing lens disposed between the plate and a butt end of the fiber, wherein optical axes of the lens and the fiber are aligned and the aperture center is position along the optical axes, and wherein the butt end of the fiber is spaces from the lens so that the fiber acceptance cone cross-sectional dimensions approximately equal to size of the aperture.
17. The instrument of claim 10, wherein the beam launch includes:
- a first plate with an aperture;
- a second plate with a pinhole aperture; and
- a focusing lens disposed between the first plate and the second plate, wherein the aperture centers are located along the optical axis of the lens.
18. The instrument of claim 10, wherein the beam translator is to translate the beam with the desired displacement in less than one millisecond.
Type: Application
Filed: Jan 16, 2012
Publication Date: Dec 19, 2013
Patent Grant number: 9256066
Applicant: Applied Precision, Inc. (Issaquah, WA)
Inventor: Jeremy R. Cooper (Issaquah, WA)
Application Number: 14/002,615
International Classification: G02B 26/08 (20060101); G02B 26/10 (20060101);